linux-kernel - RE: [patch 3/9] LTTng instrumentation tasklets

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Message-ID: <alpine.DEB.2.00.0903251351440.5675@gandalf.stny.rr.com>
Date:	Wed, 25 Mar 2009 13:52:33 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Chetan.Loke@...lex.Com
cc:	peterz@...radead.org, mingo@...e.hu, mathieu.desnoyers@...ymtl.ca,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	ltt-dev@...ts.casi.polymtl.ca, fweisbec@...il.com,
	jbaron@...hat.com, tglx@...utronix.de, rmk+lkml@....linux.org.uk,
	mhiramat@...hat.com, fche@...hat.com, haoki@...hat.com,
	t-nishiie@...css.fujitsu.com, eduard.munteanu@...ux360.ro
Subject: RE: [patch 3/9] LTTng instrumentation tasklets


On Wed, 25 Mar 2009, Chetan.Loke@...lex.Com wrote:

>  
> 
> > -----Original Message-----
> > From: Peter Zijlstra [mailto:peterz@...radead.org] 
> > Sent: Wednesday, March 25, 2009 10:18 AM
> > To: Loke,Chetan
> > Cc: mingo@...e.hu; mathieu.desnoyers@...ymtl.ca; 
> > akpm@...ux-foundation.org; linux-kernel@...r.kernel.org; 
> > ltt-dev@...ts.casi.polymtl.ca; fweisbec@...il.com; 
> > jbaron@...hat.com; tglx@...utronix.de; 
> > rmk+lkml@....linux.org.uk; mhiramat@...hat.com; 
> > fche@...hat.com; haoki@...hat.com; 
> > t-nishiie@...css.fujitsu.com; rostedt@...dmis.org; 
> > eduard.munteanu@...ux360.ro
> > Subject: RE: [patch 3/9] LTTng instrumentation tasklets
> > 
> > On Wed, 2009-03-25 at 06:52 -0700, Chetan.Loke@...lex.Com wrote:
> > > Quick question. I understand this is unrelated to this patch. So I 
> > > apologize in advance.
> > > Ingo - you mentioned "tasklets are a legacy mechanism". Is there a 
> > > plan to phase them out ? Let me draw a small picture as to what's 
> > > bothering me.
> > > 
> > > With the SR-IOV support if there are 'N' virtual functions 
> > then there 
> > > will be 'N' driver instances(actually N+1, 1 for the PF). If that 
> > > driver drains the responses in the interrupt context then all such 
> > > VF-instances could virtually block everyone else(because 
> > SR-IOV guys 
> > > might also have MSI-X enabled).
> > > So now all such drivers should alter their Rx path.Driver's 
> > can queue 
> > > tasklets and can also get the performance they want.
> > > 
> > > Any suggestions?
> > 
> > Threaded interrupts?
> > 
> 
> If we truly need to address performance and scalability for the SCSI-subsystem then we need something lightweight.

Threaded interrupts are actually quite light.

-- Steve

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